linux-toradex.git/kernel/sched/ext.c, branch v6.18-rc2

Revert "sched_ext: Use rhashtable_lookup() instead of rhashtable_lookup_fast()"

2025-09-24T06:38:23+00:00

This reverts commit c8191ee8e64a8c5c021a34e32868f2380965e82b which triggers
the following suspicious RCU usage warning:

[    6.647598] =============================
[    6.647603] WARNING: suspicious RCU usage
[    6.647605] 6.17.0-rc7-virtme #1 Not tainted
[    6.647608] -----------------------------
[    6.647608] ./include/linux/rhashtable.h:602 suspicious rcu_dereference_check() usage!
[    6.647610]
[    6.647610] other info that might help us debug this:
[    6.647610]
[    6.647612]
[    6.647612] rcu_scheduler_active = 2, debug_locks = 1
[    6.647613] 1 lock held by swapper/10/0:
[    6.647614]  #0: ffff8b14bbb3cc98 (&rq->__lock){-.-.}-{2:2}, at:
+raw_spin_rq_lock_nested+0x20/0x90
[    6.647630]
[    6.647630] stack backtrace:
[    6.647633] CPU: 10 UID: 0 PID: 0 Comm: swapper/10 Not tainted 6.17.0-rc7-virtme #1
+PREEMPT(full)
[    6.647643] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    6.647646] Sched_ext: beerland_1.0.2_g27d63fc3_x86_64_unknown_linux_gnu (enabled+all)
[    6.647648] Call Trace:
[    6.647652]  
[    6.647655]  dump_stack_lvl+0x78/0xe0
[    6.647665]  lockdep_rcu_suspicious+0x14a/0x1b0
[    6.647672]  __rhashtable_lookup.constprop.0+0x1d5/0x250
[    6.647680]  find_dsq_for_dispatch+0xbc/0x190
[    6.647684]  do_enqueue_task+0x25b/0x550
[    6.647689]  enqueue_task_scx+0x21d/0x360
[    6.647692]  ? trace_lock_acquire+0x22/0xb0
[    6.647695]  enqueue_task+0x2e/0xd0
[    6.647698]  ttwu_do_activate+0xa2/0x290
[    6.647703]  sched_ttwu_pending+0xfd/0x250
[    6.647706]  __flush_smp_call_function_queue+0x1cd/0x610
[    6.647714]  __sysvec_call_function_single+0x34/0x150
[    6.647720]  sysvec_call_function_single+0x6e/0x80
[    6.647726]  
[    6.647726]  
[    6.647727]  asm_sysvec_call_function_single+0x1a/0x20

Reported-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Merge branch 'for-6.17-fixes' into for-6.18

2025-09-23T19:10:20+00:00

Pull sched_ext/for-6.17-fixes to receive:

 55ed11b181c4 ("sched_ext: idle: Handle migration-disabled tasks in BPF code")

which conflicts with the following commit in for-6.18:

 2407bae23d1e ("sched_ext: Add the @sch parameter to ext_idle helpers")

The conflict is a simple context conflict which can be resolved by taking
the updated parts from both commits.

Signed-off-by: Tejun Heo

sched_ext: Misc updates around scx_sched instance pointer

2025-09-23T19:03:26+00:00

In preparation for multiple scheduler support:

- Add the @sch parameter to find_global_dsq() and refill_task_slice_dfl().

- Restructure scx_allow_ttwu_queue() and make it read scx_root into $sch.

- Make RCU protection in scx_dsq_move() and scx_bpf_dsq_move_to_local()
  explicit.

v2: Add scx_root -> sch conversion in scx_allow_ttwu_queue().

Reviewed-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Drop scx_kf_exit() and scx_kf_error()

2025-09-23T19:03:26+00:00

The intention behind scx_kf_exit/error() was that when called from kfuncs,
scx_kf_exit/error() would be able to implicitly determine the scx_sched
instance being operated on and thus wouldn't need the @sch parameter passed
in explicitly. This turned out to be unnecessarily complicated to implement
and not have enough practical benefits. Replace scx_kf_exit/error() usages
with scx_exit/error() which take an explicit @sch parameter.

- Add the @sch parameter to scx_kf_allowed(), scx_kf_allowed_on_arg_tasks,
  mark_direct_dispatch() and other intermediate functions transitively.

- In callers that don't already have @sch available, grab RCU, read
  $scx_root, verify it's not NULL and use it.

Reviewed-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Add the @sch parameter to scx_dsq_insert_preamble/commit()

2025-09-23T19:03:26+00:00

In preparation for multiple scheduler support, add the @sch parameter to
scx_dsq_insert_preamble/commit() and update the callers to read $scx_root
and pass it in. The passed in @sch parameter is not used yet.

Reviewed-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Drop kf_cpu_valid()

2025-09-23T19:03:26+00:00

The intention behind kf_cpu_valid() was that when called from kfuncs,
kf_cpu_valid() would be able to implicitly determine the scx_sched instance
being operated on and thus wouldn't need @sch passed in explicitly. This
turned out to be unnecessarily complicated to implement and not have
justifiable practical benefits. Replace kf_cpu_valid() usages with
ops_cpu_valid() which takes explicit @sch.

Callers which don't have $sch available in the context are updated to read
$scx_root under RCU read lock, verify that it's not NULL and pass it in.

scx_bpf_cpu_rq() is restructured to use guard(rcu)() instead of explicit
rcu_read_[un]lock().

Reviewed-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Add the @sch parameter to __bstr_format()

2025-09-23T19:03:26+00:00

In preparation for multiple scheduler support, add the @sch parameter to
__bstr_format() and update the callers to read $scx_root, verify that it's
not NULL and pass it in. The passed in @sch parameter is not used yet.

Reviewed-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Separate out scx_kick_cpu() and add @sch to it

2025-09-23T19:03:26+00:00

In preparation for multiple scheduler support, separate out scx_kick_cpu()
from scx_bpf_kick_cpu() and add the @sch parameter to it. scx_bpf_kick_cpu()
now acquires an RCU read lock, reads $scx_root, and calls scx_kick_cpu()
with it if non-NULL. The passed in @sch parameter is not used yet.

Internal uses of scx_bpf_kick_cpu() are converted to scx_kick_cpu(). Where
$sch is available, it's used. In the pick_task_scx() path where no
associated scheduler can be identified, $scx_root is used directly. Note
that $scx_root cannot be NULL in this case.

Reviewed-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Add SCX_EFLAG_INITIALIZED to indicate successful ops.init()

2025-09-23T19:03:26+00:00

ops.exit() may be called even if the loading failed before ops.init()
finishes successfully. This is because ops.exit() allows rich exit info
communication. Add SCX_EFLAG_INITIALIZED flag to scx_exit_info.flags to
indicate whether ops.init() finished successfully.

This enables BPF schedulers to distinguish between exit scenarios and
handle cleanup appropriately based on initialization state.

Acked-by: Andrea Righi 
Signed-off-by: Tejun Heo

sched_ext: Fix stray scx_root usage in task_can_run_on_remote_rq()

2025-09-23T19:03:26+00:00

task_can_run_on_remote_rq() takes @sch but it is using scx_root when
incrementing SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE, which is inconsistent and
gets in the way of implementing multiple scheduler support. Use @sch
instead. As currently scx_root is the only possible scheduler instance, this
doesn't cause any behavior changes.

Acked-by: Andrea Righi 
Signed-off-by: Tejun Heo